My 17" FZR rear wheel mod.

[1tinindian]

FJmonkey  (what the hell is your real name?)

I agree, this has been a very good learning topic for me.

I did just talk to a shop owner tonight that can make me some dog bones, but the best SS he has is 304.

From what you said ealier, that's not really up to the task either?

Arnie and Pat, good feedback, thanks for you input!

Leon

[FJmonkey]

FJmonkey  (what the hell is your real name?)

I agree, this has been a very good learning topic for me.

I did just talk to a shop owner tonight that can make me some dog bones, but the best SS he has is 304.

From what you said ealier, that's not really up to the task either?

Arnie and Pat, good feedback, thanks for you input!

Leon

Hey Leon, my name is Mark. As I read more on what steels others have used for their bones I am thinking that HRPO and 304 SST sheet may have enough tensile strength. As these steels are softer than others and lacking any testing data I can only recommend inspecting custom bones as often as one changes the rear tire. As time goes on with any lack of change in the bones then you can feel more confident in the material of choice. I hope I have not caused any panic on this. My experience with mild steel like HRPO I know is quite soft and hate the thought of anyone (club member or not) having a bad moment on two wheels. Ounce of caution..... 304 has excellent corrosion resistance, avoid the bunny hop whenever possible and ride safe.

[Pat Conlon]

Metallurgy aside, in looking at the actual design, you can draw some conclusions.
Assuming that the links would fail under tension, the area it would likely fail would be area with the least amount of material that would be available to resist the tension. Makes sense, right? See how the oem dogbones are designed? See the uniform material thickness around the bolt holes?
If you drew a straight line from the center of the holes to the outside edge, see how thick the material is at these two points on the oem links? i.e. The distance from the edge of the hole to the outside edge of the link.

Leon, now look at the ones you fabricated. See the thinner sections? If they fail, that's where your new links will fail.

[1tinindian]

Thanks Mark.
No panic, just concern that I'm creating a problem for myself when it could be just as easily eliminated by doing it right the first time.
I like the idea of the corrosion resistance of the 304SS, so I think I'm going to go ahead and have those made.
I'll assume that they can still be made out of 1/4"x 1" material, correct?

It's been good getting to know you Mark, and I hope we have added some valuable information to the forum on this subject.
After all, safety is every ones #1 concern where motorcycles are concerned.

Leon

[1tinindian]

All very good points Pat.
I don't mind being so heavily scutinized on this subject as long as some others may benefit from it.
I only wish this topic had been covered in this great of detail (including pictures), prior to me needing to make these parts.

If you don't mind, I'd like to quote you from a thread entitled "Dogbones - raising rear end," from 2009, where you said,

"  Go ahead and do the bones, it's easy, you can get the steel stock at Lowe's/Home Depot. Cut the strap iron to length and drill the holes. Easy peesey. I did have to special order a metric drill bit for the holes (sorry, I can't remember the size) Hint: when you drill the holes, clamp both pieces together in a vise and drill both pieces at the same time. That way your holes will line up dead nuts with both pieces. *A important point*

Don't over think the mod, it's sooo easy."

So you can see where I might have been just a little confused over this, after all, I didn't over think it.
I just cut the metal to length and drilled two holes in it.

Cheers,
Leon

[andyb]

Aftermarket dogbones are frequently aluminum.  Yes, in a massive wreck (or a big Evel Knievel jumps), they'll bend.  So?  I understand that occasionally it'll be the difference between riding home and trailering home, but after that much force going through things, I would greatly prefer trailering it home and doing a good inspection on it, rather than one done while you're a little shaken up on the roadside thinking "well, it looks good enough....".

My FJ wears Soupy links, which are really a good compromise imo, and the adjustability is lovely.  My ZX9 wears aluminum dogbones (6064, I think) and haven't shown any sign of even beginning to bend.  At the track, I frequently see guys with vastly extended swingarms (better leverage against the linkages with a longer lever, remember) and aluminum dogbones, and have never seen a failure that could be directly attributed to the dogbones. 

Don't worry so much.  I do agree with clamping them together and drilling both at once, to ensure you get the length exactly the same.  Aluminum works fine, but stainless would polish up nicely and be easy to keep clean.  Steel would be fine if you paint or powder it to prevent rust.

[rktmanfj]

[FJmonkey]

This is precisely what Pat described as the failure mode. You can see that the holes were not centered on these links. The top link on the Left is off center as well. The thinner side stretched faster than the thicker side. Once the thin side broke free the end of the link rotated around like pealing of the top of a tin can. The thin side bent towards the center of the link, the thick side bent away from it. Good image to show how material thickness and shape is as important as material selection.

FYI, 6061-T6 Aluminum has a tensile strength near 42Ksi and 7075-T6 is between 74 and 78Ksi. If weight is really important then stick with the 7075-T6.

[rktmanfj]

The holes were indeed centered when they were drilled...  there is more deformity there than the pic really shows.  They are off on every dimension, but they were subjected to pretty large force.

[FJmonkey]

The holes were indeed centered when they were drilled...

Then the Left side must have stretched as well. Makes sense, same forces at both ends, both sides gave out some but once stretched enough, one side became the weakest and lost.

[rktmanfj]

It was not exactly an even hit, so I would say you are right.

Nice of folks not to bring this up again, but I guess I will man up and do it.    

http://www.fjowners.com/index.php?topic=2792.0

[andyb]

Exactly why I think Evel himself would be proud! 

I do wonder though:  Had they been stock, would the impact have broken something else?  Twisted the swingarm, for example?  That failure is the only one that I've honestly ever heard of, ever, from anyone wadding a bike up, aftermarket, stock, or homemade dogbones.  It's a rare enough thing that I guess I just don't worry it.  I'm more concerned that a tire will decide to fall off its' bead or delaminate (both of which I've heard of happening more than a couple times).

I also wonder if changing the length altered the ratio of how the linkage works.  It's a rising rate if memory serves, and yet all the aluminum dogbones that I know of are used in a lowering rather than raising application.  Someone with more time than me want to work out the forces involved and see what happened?

(I'd do the math, but my computer has recently decided that it wants to be a ball gown, or a potato, or anything other than a computer, so I'm distracted and fighting it currently... sigh...)

[tmkaos]

Hi guys - just thought I'd throw in my 2 cents worth here..

I'm an engineer, spend all my days for the past 12 years running lathes and mills so that's where my experience comes from..

If you're making up dog bones at home, you can be smart about it and make a pretty damn decent job that will A: look pretty good and B: help it to not fail


For starters, things to remember regardless of your material choice, that sharp edges, ragged holes and as mentioned before, uneven hole spacing are all things that create stress points and fractures start from.

Have a damn good look to see where you can get away with leaving material on the dogbones - especially around the holes and ends. Don't be too skimpy - how much do these things weigh anyway? 

Measure carefully - measure twice cut once


Make yourslf up a scriber - if you can't buy one, sharpen up the opposite end of a small dia drill into one, you can do it just with a hand held grinder if you don't have a bench grinder.

Scribe out the shape you want - ruler if it's straight lines or even trace around something round for curves etc

Get a ruler and after you've cut your dogbones to the shape, measure out with a ruler where you want the holes then use the scribe as a dot punch and give it a good whack to help you locate those holes. The drill will stick in the dot and go thru on centre every time no wandering. Also pre-drill with small drill first - don't whack through the big drill, it will go better with a pilot hole.

Chamfer every sharp edge including the drilled holes - less stress points = stronger.

Driling them together is another excellent idea.

You can drill before you cut them out if you want if it makes it easier to hold in a vice, no hard and fast rules about that...


The one bit of advice to remember above all else that has stood me in good stead is KISS!
  KEEP IT SIMPLE, STUPID!
Don't overcomplicate - it doesn't need it.


I know a lot of you guys are competent engineers and are very capable of making things, there's some awesome bikes on here but sometimes there are a few tricks that can escape the first timers...

Cheers,

James

[Pat Conlon]

...I just cut the metal to length and drilled two holes in it.

No worries Leon, I would have used wider bar stock, so I had more material between the edge of the holes and the outside edge of the stock.  Pat

[1tinindian]

...I just cut the metal to length and drilled two holes in it.

No worries Leon, I would have used wider bar stock, so I had more material between the edge of the holes and the outside edge of the stock.  Pat

I have a drawing made up for a better pair of bones.
I'll either make them myself out of steel, or have the machine shop make some out of SS.

Either way, my riding for this year is pretty much over with, so I will have plenty of time to get them made by next spring.

Leon